The Sloane Letters have several references to eighteenth-century patients drinking asses’ milk. It was never held up as an elixir of life, but was thought to be particularly useful in treating lung ailments (as with the Viscount Lymington in 1722), blood problems (in the case of Catherine Henley) and emotional troubles (the Duchess of Beaufort’s hysteria in 1705). But one thing that always intrigued me was the lengths to which patients would go to get asses’ milk; why, I wondered, did it seem like such a faff to find a lactating donkey?

In 1723, Robert Holdwsorth reported that Lady Middleton had provided his wife with a goat and an ass so she could drink milk, as per Hans Sloane’s prescription. Mrs Holdsworth had stopped drinking the milk, though, as it disagreed with her. (A common complaint!) On its own, this might just seem like an act of kindness on Lady Middleton’s part—but it was likely darned helpful for the Holdsworths to have a friend in high places who could help in finding an ass.

The Duke of Bedford, for example, wanted to drink asses’ milk in 1724, as Sloane had recommended for an eye problem. Unfortunately, the Duke had been unable to procure an ass in the country and had needed to send to Streatham (another family holding) for one. As the letter was sent from his seat at Woburn Abbey in Bedfordshire and Streatham is over fifty miles away in Surrey, the ass came from quite a distance.

As Sally Osborn tells us at The Recipes Project, there are lots of eighteenth-century recipes for artificial asses’ milk. One version included snails boiled in milk with eringo root and brown sugar. Yum.

Donkey milk is good stuff, by several counts, being the closest in composition to human milk. Although early modern people wouldn’t have known these details, Sloane and other physicians prescribed it regularly and patients were often curious to try it. Mrs Reynolds wondered in 1725 whether Sloane might recommend that she try asses’ milk to help her general weakness. He did, as he scrawled “lact. asen.” on her letter.

It turns out that asses’ milk is still hard to get today. Across Europe, the average price is over £40 per litre. Female donkeys produce only a litre of milk per day for about half they ear and can only produce milk when its foal is nearby. Not the easiest of milk to acquire… The eighteenth-century demand, it seems, outstripped supply. No wonder patients struggled to find lactating asses and settled for unappealing substitutes!